Superconducting structures may be seen as advantageous since they enable conducting current without resistive losses. Superconducting structures, such as superconducting tapes are thus being used for a number of applications, such as generators and transformers. However, although they possess excellent properties when carrying direct current, they may exhibit high losses when used in alternating current (AC) applications.
Means of reducing AC losses that are currently available may not in a straightforward manner be adapted to processing long lengths of superconducting tape.
In the application U.S. Pat. No. 7,593,758 B2 there is presented a tape which has a high temperature superconductor layer that is segmented. Disruptive strips, formed in one of the tape substrate, a buffer layer, and the superconducting layer create parallel discontinuities in the superconducting layer that separate the current-carrying elements of the superconducting layer into strips or filament-like structures. Segmentation of the current carrying elements has the effect of reducing AC losses. Methods of making such a superconducting tape and reducing AC losses in such tapes are also disclosed.
In the application U.S. Pat. No. 4,101,731 there is presented a composite multifilament superconducting structure is provided, which includes an elongated substrate-carrying, longitudinally-directed, sputtered discrete filament of an A-15 type intermetallic superconductor. In a preferable procedure, a plurality of spaced, generally longitudinal grooves are formed on the surface of an elongated filamentary substrate, preferably a metal wire. The walls of the grooves on the substrate surface are shaped to undercut the curvilinear surface of the substrate located between two adjacent grooves so that at least some of the wall portions of the grooves are geometrically shadowed during the subsequent sputtering step in which a superconductor is sputtered onto the substrate. In particular, a film of a suitable superconducting intermetallic compound having A-15 crystalline structure, such as Nb3Ge, is thereupon sputtered onto the grooved substrate and deposits at the bottom of the grooves and at the surface portions of the substrate between grooves. The shadowed wall portions remain substantially deposit-free so that the resultant spaced deposits extend as distinct lines or bands along the substrate to thereby constitute the superconductive filaments. A plurality of such substrates may, if desired, be consolidated into a further composite structure, by bundling the substrates and passing same through a molten metal. The resultant structure may then be sized to yield as a foral product a composite of the substrates bearing the superconducting filaments in a surrounding matrix of the metal.
It may be seen as a problem with the prior art methods that they are not adaptable to continuous processing of long lengths of such tape, effective, cheap, enabling low material consumption and/or provides a good substrate for a superconducting tape. It would be advantageous to have a method for making a substrate for a superconducting tape having reduced AC losses, wherein the method is adaptable to continuous processing of long lengths of such tape and which method would be effective, cheap and/or would be a method which provided an improved substrate for a superconducting tape compared to the prior art.